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A new study looks at links between psychiatric disorders and diabetes. Sergey Filimonov/Stocksy
  • Researchers recently investigated the link between diabetes and psychiatric conditions.
  • They found that people with psychiatric disorders are more likely than the general population to have type 2 diabetes.
  • They say that further research is needed to investigate the underlying mechanisms behind the link.

Psychiatric conditions are common, can reduce quality of life, and are linked to higher mortality rates from suicide, accidents, and comorbidities.

Previous research has shown that people with bipolar disorder, schizophrenia, and major depression have higher rates of type 2 diabetes than the general population.

According to the World Health Organization (WHO), the number of people with diabetes rose from 108 million in 1980 to 422 million in 2014. Scientists expect rates of the condition to continue to increase in the coming decades.

Understanding how and if type 2 diabetes connects to various psychiatric conditions could help policymakers and healthcare professionals manage both conditions.

In a recent study, an international collaboration of researchers led by the University of Southern Denmark conducted a meta-analysis of 32 systematic reviews detailing 245 primary studies to understand the possible links between psychiatric conditions and type 2 diabetes.

The researchers found that people with one of many psychiatric disorders, including sleep disorders, binge eating disorders, and anxiety disorders, tend to have higher rates of type 2 diabetes than the general population.

“The prevalence of type 2 diabetes in people with a psychiatric disorder has been studied by numerous research groups in the last decades,” Nanna Lindekilde, first author of the study and a doctoral candidate at the Department of Psychology at the University of South Denmark, told Medical News Today.

“Our umbrella review summarizes the findings from studies that had been published from 1980 until 2020.”

“However, it is interesting to see that across all the investigated psychiatric disorders, we see a relatively high prevalence of type 2 diabetes. Previously, most research had particularly focused on individuals with, [for example], schizophrenia or depression, but our review highlights the importance to focus on a broader range of psychiatric disorders,” she added.

MNT also spoke with Mercedes Carnethon, Ph.D., vice-chair of preventative medicine at Northwestern University Feinberg School of Medicine, who was not involved in the study. She said, “These findings are not surprising given what we have seen as a high prevalence of a variety of psychiatric disturbances among people with diabetes.”

“What is new about this work is the scale of it,” she explained. “The summary of reviews and the meta-analyses brings together data across multiple smaller studies to generate estimates of the burden that reflect a diversity of study participants from multiple different regions of the world and settings. These findings highlight the scale of the problem.”

The study appears in Diabetologia.

The researchers searched four online databases, including PubMed and the Cochrane Database of Systematic Reviews. The focused on systematic reviews of observational studies investigating the prevalence of type 2 diabetes and psychiatric disorders.

Among all the studies, researchers identified cases of diabetes and psychiatric conditions via:

  • diagnosis
  • diagnostic interviews
  • hospital records
  • medicine prescriptions
  • self-reports

The researchers selected 32 systematic reviews involving 245 primary studies for analysis. All health records involved in the study were from adults aged 18 and over.

Nineteen of the reviews were from Europe, six were from the United States, four were from Australia, and one each from Chile, China, and Ethiopia. The reviews included in the analysis focused on 11 categories of psychiatric conditions:

From meta-analyses of the reviews in relation to each of the psychiatric conditions above, the researchers found that people with sleep disorders have the highest prevalence of type 2 diabetes.

They found that 39.7% of people with a sleep disorder have type 2 diabetes, while the same is true for:

  • 20.7% of those with binge eating disorder
  • 15.6% of those with a substance use disorder
  • 13.7% of those with an anxiety disorder
  • 11.4% of those with bipolar disorder
  • 11.1% of those with psychosis
  • 8.1% of those with an intellectual disability

The researchers noted, however, that there was a substantial publication bias in four of the meta-analyses focusing on schizophrenia, substance use disorder, binge eating disorder, and mixed psychiatric disorders.

Altogether, they found that 20 of the systematic reviews had a high risk of bias regarding the identification and selection of included studies, data collection, and study appraisal.

When accounting for all systematic reviews, the researchers found that prevalence estimates for type 2 diabetes among those with psychiatric conditions ranged from 1.3% to 66%.

Meanwhile, when only accounting for the reviews with a low risk of bias, estimates of type 2 diabetes ranged from 5.1% to 22.3%.

Scientists do not understand the underlying mechanisms for the link between diabetes and psychiatric conditions. They are likely to be bidirectional.

“Most of these studies assess both diabetes and the psychiatric disorders at one point in time, which means we don’t know whether diabetes precedes or follows these psychological disturbances,” said Dr. Carnethon.

“For example, sleep disorders, substance use disorder, and anxiety can be a consequence of the burden of managing a life changing disease such as diabetes.”

“At the same time, each of these conditions can cause changes in the brain and in the body’s way of processing food for energy. Those changes in how the body processes and uses food for energy define our metabolism. Diabetes is a metabolic disturbance,” she continued.

Lindekilde expanded on the bidirectional nature of psychiatric conditions and type 2 diabetes:

“For several psychiatric disorders, a bidirectional association between psychiatric disorders and type 2 diabetes has been observed. This is the case for depression, for example. People with depression have a higher risk of developing type 2 diabetes, but that the reverse is also true: people with type 2 diabetes more often develop depression.”

“We believe that the risk for developing type 2 diabetes is increased for most psychiatric disorders. In a nationwide, register-based cohort study just accepted for publication in Diabetes Care, we followed more than five million individuals from 1995–2018, and we detected an increased risk of incident type 2 diabetes across all categories of psychiatric disorders,” she added.

“We believe that a combination of [lifestyle factors] — e.g., [difficulty eating a balanced diet], smoking, physical inactivity, and [inadequate sleep] — use of psychotropic medication, comorbidities, as well as various biological factors, e.g., genetics, explains why type 2 diabetes is more prevalent as well as incident in individuals with a psychiatric disorder,” she explained.

The researchers concluded that future research should investigate the link between type 2 diabetes and a “full range” of psychiatric conditions.

They also note some limitations to their work. They explain that, as the studies included in their review took place over several decades, the prevalence estimates for type 2 diabetes in people with psychiatric disorders may not be as relevant today.

They also note that there were no available studies detailing some common conditions, such as attention deficit disorders and autism.

“Our review is based on existing systematic reviews investigating the prevalence of type 2 diabetes in individuals with a psychiatric disorder,“ said Lindekilde. “Thus, our findings are limited by the quality and content of existing systematic reviews published prior to our search.”

“If the review had been conducted based on primary studies rather than systematic reviews, additional categories of psychiatric disorders would probably have been included. However, we don’t expect that this would have changed our main finding: that individuals with a psychiatric disorder have a relatively high prevalence of type 2 diabetes,” she concluded.

“People with a severe psychiatric disorder, such as schizophrenia, on average live 15 years shorter,” explained Lindekilde.

“One of the mechanisms that explain this might be the development of type 2 diabetes and suboptimal detection and suboptimal treatment of diabetes. Our findings again highlight the importance of focusing on type 2 diabetes risk and type 2 diabetes treatment in individuals with a psychiatric disorder.”

“From previous research, we know that early detection and subsequent early treatment is important to minimize and/or delay the complications of type 2 diabetes. Furthermore, our findings highlight that more research is needed to understand the high prevalence of type 2 diabetes in this population,” she added.

“In an ongoing study with more than 250,000 individuals, we investigate potential mediating mechanisms that may explain the association between a broad range of psychiatric disorders and incident type 2 diabetes. We need to learn more regarding which mediating mechanisms play the biggest role and to explore whether the mechanisms differ across the different categories of psychiatric disorders.”

“Knowledge regarding the mechanisms is important and needed in future prevention initiatives,” she concluded.

“Diabetes is a life changing and life threatening disease. Its proper management can stop some of the devastating consequences,” said Dr. Carnethon.

“This paper highlights that we must address potential upstream psychological disturbances so that patients are mentally equipped to implement the intense and often burdensome strategies to manage their diabetes.”

– Dr. Carnethon